Disease Cases Climb; Cause Remains Elusive

Postweaning multisystemic wasting syndrome is considered an emerging disease complex. But no one seems really sure of all the factors involved.The Iowa State University (ISU) diagnostic laboratory announced recently that postweaning multisystemic wasting syndrome (PMWS) is an emerging pig disease complex. Cases jumped from single digits to more than 500 in the first nine months of 2000 (see Figure

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Postweaning multisystemic wasting syndrome is considered an emerging disease complex. But no one seems really sure of all the factors involved.

The Iowa State University (ISU) diagnostic laboratory announced recently that postweaning multisystemic wasting syndrome (PMWS) is an emerging pig disease complex. Cases jumped from single digits to more than 500 in the first nine months of 2000 (see Figure 1).

"PMWS tends to be a grow-finish disease with the onset of most cases occurring between 10-14 weeks of age," reports Pat Halbur, DVM, pathology section leader at the ISU lab.

"However, the duration of the disease within a system varies. It's often just a single batch problem in smaller herds that use internal gilt replacement and all-in, all-out pig flow," he says.

"But, there are an increasing number of cases where PMWS has become endemic in multiple building finishing sites run on a continuous-flow basis," he adds.

While those observations are cause for concern, they tell only part of the story.

"For some individual herds, PMWS has been a frustrating problem. For the U.S. pork industry as a whole, it's a relatively minor disease problem, compared for instance, to PRRS (porcine reproductive and respiratory syndrome). We need to keep in mind that part of the reason we're finding more cases of PMWS is that we're looking for it and have developed tools to diagnose PMWS," offers Steve Sorden, DVM, ISU diagnostic laboratory.

Cause up for Grabs Porcine circovirus type 2 (PCV2) has been mentioned as the main cause of PMWS. PCV2 is not a new virus. It appears to be widespread, and almost every herd seems to be infected.

But, only a small fraction of herds infected with PCV2 appear to have PMWS. Therefore, something else must be triggering the complex, relates Sorden.

Experts speculate that the recent emergence of this viral pathogen is the work of management or other animal health changes.

Where PCV2 is present, it appears to make diseases like PRRS worse. Five to 10% of the pigs in a group going through PRRS/porcine respiratory disease complex waste away and die, explains Sorden.

James Collins, DVM, director of the University of Minnesota's diagnostic laboratory, also questions the role of PCV2.

"We can identify PCV2 quite readily in our lab now because we've developed new diagnostic tools to find it. That does not mean just because our numbers are increasing that there is a major epidemic of any kind," says Collins.

Most of the PMWS cases at Minnesota are associated with other pathogens, especially PRRS.

Thirty-three cases of PMWS were identified last year at the Illinois diagnostic lab at Galesburg, reports director Douglas Hoefling, DVM. Of that total, seven were PCV2 infection only. The rest were a mixed infection, the majority with PRRS and a sprinkling of other viral and bacterial problems, he reports.

Furthermore, half of the 33 cases at the Illinois lab had circovirus lesions of the lymphoid organs.

The infection rate is probably much higher than that figure, says Hoefling. But when we look at the levels of actual disease caused by PCV2, it's probably as low as 1% or so.

In Illinois, pigs infected with PMWS were generally 5-12 weeks of age, with a few more than 16 weeks of age.

PRRS was implicated in more than 50% of the PMWS cases diagnosed at the ISU lab, says Sorden.

Positive Diagnosis Serology may be of limited value in determining if your herd has PMWS, explains Hoefling. He advises getting at least three to four pigs posted and submitted to the diagnostic lab to look for lesions in lymphoid tissues and to do a variety of tests for other infectious agents.

"Submit several pigs that are representative of the true clinical history of the problem," he suggests.

Getting a correct diagnosis is complicated by co-infections with PRRS and Mycoplasmal pneumonia, says Halbur. That enables PMWS to mimic other diseases.

There are three requirements for a positive diagnosis of PMWS, stresses Sorden. Pigs must show clinical signs, have lymphoid lesions and be diagnosed with PCV2 infection.

Treatment Options There is no vaccine for PMWS. Halbur suggests focusing on biosecurity, proper sanitation and prevention and treatment of co-infection with other pathogens.

Sorden says that some practitioners report that aspirin and other anti-inflammatory drugs appear useful in treatment. At least two companies are working on a PCV2 vaccine to prevent PMWS.

A large team of scientists at the ISU College of Veterinary Medicine is conducting research to better understand the cause(s) of PMWS and to identify control measures for this disease complex.

After more than 50 years of control and eradication efforts, brucellosis is almost eradicated from U.S. livestock herds.

Only two infected cattle herds are left. Surprisingly, swine brucellosis still remains. Only a handful of hog herds have been identified as infected in the past decade or so.

This past year was a different story. There were 55 newly infected swine herds found in fiscal year 2000. That compares with 18 during the previous fiscal year, according to a report at the U.S. Animal Health Association annual meeting. One herd in Texas remains infected. Some 54 herds in eight states were depopulated at a cost of $173,617.

Brucellosis is a bacteria that causes pregnant livestock to abort, sickens young animals, cuts milk production and interrupts breeding cycles.